<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .rectangle {
            position: relative;
            width: 250px;
            height: 120px;
            background-color: skyblue;
        }
        .rectangle .triangle {
            position: absolute;
            right: -30px;
            top: 0;
            bottom: 0;
            margin: auto 0;
            width: 0px;
            height: 0px;
            border: 15px solid transparent;
            border-left-color: skyblue;
        }
    </style>
</head>
<body>
    <div class="rectangle">
        <div class="triangle"></div>
    </div>
</body>
</html>